The future wireless communication or cellular system is required to increase the coverage range and to support higher speed transmission, which presents new challenges to the wireless communication technique. Meanwhile, the issue of system construction and maintenance expenses is even more prominent. With the increase of the transmission rate and communication distance, the battery energy consumption issue has also become prominent, and the future wireless communication will use higher frequencies, which results in more severe path loss attenuation. In order to increase the high data rate, group mobility and coverage range of the temporary network deployment, to improve cell edge throughput, and to provide services for users within the coverage holes of the cellular system, the wireless communication system introduces the Relay technique, and therefore, the relay technique is considered as a crucial technique of the 4G.
In the Long Term Evolution (LTE) communication system, a Physical Downlink Control Channel (PDCCH) is designed to be composed of a plurality of different components, and each component has its own specific functions. A plurality of terms and conventions is defined in the following for a convenience of description:
1. Resource Element (RE): the minimum time and frequency resource block, which occupies 1 subcarrier in 1 Orthogonal Frequency Division Multiplexing (OFDM) symbol.
2. Resource Element Group (REG): 1 REG can be composed of 4 or 6 REs according to different positions of the reference symbol in each OFDM symbol.
3. Control Channel Element (CCE): the CCE is composed of 36 REs, 9 REGs, and the CCE comprises information such as: the user's downlink scheduling grant information (DL grant) and the uplink scheduling grant information (UL grant), as well as information related to the system information (SI), random access (RA) response and paging.
4. Physical Resource Block (PRB): 1 continuous slot in the time domain, and 12 consecutive sub-carriers in the frequency domain.
5. PRB pair: 1 continuous subframe in the time domain, and 12 consecutive sub-carriers in the frequency domain.
6. Aggregation level L: a combination format of CCEs, that is, the PDCCH can only be composed of L CCEs, where L{1,2,4,8}. That is to say that the PDCCH only is composed of the combination of 1 CCE (denoted by 1-CCE), the combination of 2 CCEs (denoted by 2-CCE), the combination of 4 CCEs (denoted by 4-CCE) or the combination of 8 CCEs (denoted by 8-CCE), and these 4 different combinations further correspond to 4 different coding rates, that is, the coding rate of the 1-CCE is ⅔, the coding rate of the 2-CCE is ⅓, the coding rate of the 4-CCE is ⅙, and the coding rate of the 8-CCE is 1/12.
7. Search Space (SS): the search space is composed of a plurality of candidate control channel groups, and the UE monitors the search space and blindly detects the downlink control channel related to this search space in the search space.
8. Two types of search spaces: one is the UE-common Search Space that all the UEs must monitor, and it bears common information related to the SI, RA response and paging; the other is the UE-specific Search Space, which bears the respective uplink and downlink scheduling grant information of UE.
9. Different CCE aggregation levels have the corresponding number of candidate control channels, namely the maximum times of blind detections. For example, in the UE-specific Search Space: the number of candidate control channels of the 1-CCE is 6, that is, the times of blind detection according to 1 CCE as a group are no more than 6; the number of candidate control channels of the 2-CCE is 6, that is, the times of blind detection according to 2 CCEs as a group is no more than 6; the number of candidate control channels of the 4-CCE is 2, that is, the times of blind detection according to 4 CCEs as a group is no more than 2; and the number of candidate control channels of the 8-CCE is 2, that is, the times of blind detection according to 8 CCEs as a group is no more than 2. In the UE-common Search Space: the number of candidate control channels of the 4-CCE is 4, that is, the times of blind detection according to 4 CCEs as a group is no more than 4; and the number of candidate control channels of the 8-CCE is 2, that is, the times of blind detection according to 8 CCEs as a group is no more than 2.
The detailed process of the UE performing blind detection on the PDCCH in the LTE system is:
at the eNB side (where eNB is also called as the E-UTRAN NodeB, where the E-UTRAN is the Evolved Universal Terrestrial Radio Access Network),
step 1: channel coding is performed on control information born in the PDCCH of each UE respectively;
step 2: the coded control information born in the PDCCHs of all the UEs is cascaded, and is scrambled with a cell-specific sequence;
step 3: Quadrature Phase Shift Keying (QPSK) modulation is performed to acquire a string of CCEs corresponding to the control information born in all the PDCCHs at this time, and the CCEs are numbered from 0; it is assumed that the PDCCH at this time is composed of 32 CCEs in total, that is, they are numbered as CCE 0, CCE 1, . . . , CCE 31:
step 4: The above string of CCEs is interleaved by taking the REG as the unit and then mapped to the RE;
step 5: the CCEs are transmitted after performing the Inverse Fast Fourier Transform (IFFT).
At the UE side,
step 1: the receiving end acquires a string of CCEs with the same numbers with those at the eNB side after performing Fast Fourier Transform (FFT) and de-interleaving;
step 2: the UE starts to the blind detection from the combination of 1-CCE, first calculates the starting position of the 1-CCE based on parameters such as the UE identity (ID), subframe number and so on, that is, the blind detection is start from the CCE with which number, and then determines the search space according to the number of candidate control channels. For example, the starting position of the 1-CCE is CCE 5, and then the search space of the UE is {CCE 5, CCE 6, CCE 7, CCE 8, CCE 9, CCE 10}. In other words, UE should perform the blind detection on [CCE 5, CCE 6, CCE 7, CCE 8, CCE 9, CCE 10] respectively.
Step 3: if the UE does not detect a UE ID matched itself when performing blind detection in accordance with the combination of 1-CCE, it starts to perform blind detection form the combination of the 2-CCE. First, the starting position of the 2-CCE is still calculated according to parameters such as its UE-ID, subframe number and so on, and then the search space is determined according to the number of candidate control channels. For example, the starting position of the 2-CCE is CCE 10, and then the search space of the UE is {[CCE 10 CCE 11], [CCE 12 CCE 13], . . . , [CCE 20 CCE 21]}. In other words, the UE should perform blind detection on [CCE 10 CCE 11], [CCE 12 CCE 13], . . . , [CCE 20 CCE 21] respectively, and so on.
Step 4: if the UE does not monitor the UE ID matched with itself in the whole blind detection process, it means there is on no control signaling to be sent to this UE, and the UE switches to sleep mode; if the UE monitors the UE ID matched with itself, it demodulates the corresponding service information in accordance with the instructions in the control signaling.
In the mobile communication system with relay nodes, as shown in FIG. 1, the link between the eNB and the RN is called as a Backhaul Link, the link between the RN and a user under its coverage range is called as an Access Link, and the link between the eNB and the UE under its coverage range is called as a Direct Link. For the eNB, the RN is equivalent to UE; and for the UE, the RN is equivalent to an eNB.
The inband relay means both the backhaul link and the access link use the same frequency band, and therefore when applying the inband relay, the RN cannot perform sending and receiving operations simultaneously in the same frequency resource in order to avoid its own sending and receiving interference. When the RN sends the downlink control information to UE which belongs to this RN, it cannot receive the downlink control information sent from the eNB. Therefore, the RN first sends the downlink control information to UE which belongs to this RN in the previous one or two OFDM symbols during the downlink transmission, then switches from transmission to reception in a certain period, and after completing the switching, receives the data from the eNB in the subsequent OFDM symbols, wherein the data include the Relay Physical Downlink Control Channel (R-PDCCH) and the Relay Physical Downlink Shared Channel (R-PDSCH), as shown in FIG. 2, namely the downlink control channel sent by the eNB to the RN is born in the Physical Resource Block (PRB).
The eNB sends the downlink control information via the R-PDCCH (the PDCCH of the Relay), and the control information born in the R-PDCCH includes information such as the uplink/downlink scheduling grant of the RN and so on. In the downlink backhaul subframe, the eNB semi-statically reserves a plurality of PRBs for the R-PDCCH transmission, as shown in FIG. 3. In the downlink backhaul subframe, the eNB semi-statically reserves a plurality of PRB pairs for the R-PDCCH transmission. Wherein, the PDCCH of the Rel-8 UE is transmitted on the previous n (n≦3) symbols in the 1st slot, the downlink scheduling grant information (DL grant) of the RN is transmitted on the rest symbols in the 1st slot except the symbol occupied by the PDCCH, and the uplink scheduling grant information (UL grant) of the RN is transmitted on the 2nd slot.
At present, the research on the R-PDCCH in the research on the Relay is always a hot spot. For the R-PDCCH detection problem, the 3rd Generation Partnership Project (3GPP( ) only has a RN-common SS similar to UE-common SS, however, there is no any solution for the R-PDCCH detection.